Growers that use supplemental co2 don't exchange the air at a "frantic" rate, there are two main reasons.
1. Adding extra co2 allows the plants to thrive and function at a higher level of metabolism - and at a higher temperature range (around 90 or 95 degrees F.). Therefore, not as much ventilation is needed because of temperature concerns.
2. The added co2 reduces the need for "fresh air" ventilation, just enough to replenish the relatively small amount of Oxygen needed (mostly by the roots). Therefore, not as much ventilation is needed because of "breathability" concerns.
The fact that there is a greatly reduced requirement for active ventilation allows the "co2 Grower" to exchange the air in his chamber at a much slower rate. This, in turn, allows the co2 to have a longer "Hang Time" so it can be "respirated" into the plant as effectively as possible. To do otherwise and just blast air through the chamber would be counter-productive to co2 augmentation, as it would just blow the carbon dioxide away!
I think this is what your question was asking about, hope this helps!
